BUZZING NOISE - AM BAND OF RADIO (INST. FILT. ON PCM/TCM). GMC Truck Jimmy

REVISION: 04/14/94

THIS BULLETIN IS BEING REVISED TO REMOVE THE LAST SENTENCE OF THE CONDITION AND TO ADD THE NOTE IN THE CORRECTION. ----------------------------------------------------------------------

SUBJECT: BUZZING NOISE IN AM BAND OF RADIO (INSTALL FILTER ON PCM/TCM)

MODELS: 1992-94 CHEVROLET AND GMC TRUCK C/K, S/T TRUCKS AND M/L, G VANS 1992-94 OLDSMOBILE BRAVADA WITH 4L60-E AND 4L80-E TRANSMISSION

CONDITION:

SOME OWNERS MAY COMMENT OF A BUZZING NOISE IN THE LOW END OF THE AM RADIO BAND WITH THE ENGINE RUNNING.

CAUSE:

THE SWITCHING OF THE FORCE MOTOR IN THE ELECTRONIC TRANSMISSION EMITS AN RFI SIGNAL THROUGH THE PCM/TCM. THE AM BAND OF THE RADIO IS RECEIVING THIS INTERFERENCE THROUGH THE ANTENNA.

CORRECTION:

TO DETERMINE IF THIS IS THE CAUSE OF THE OWNER'S COMMENTS, FIRST DUPLICATE THE CONDITION AND THEN DISCONNECT THE ELECTRICAL CONNECTOR AT THE TRANSMISSION (THIS WILL DISABLE THE FORCE MOTOR). IF THE CONDITION IMPROVES, INSTALL AN IN-LINE FILTER (P/N 1224205) TO THE IGNITION LEAD (CKT 439) OF THE PCM/TCM. SOME APPLICATIONS MAY HAVE TWO (439 CKT), IN WHICH CASE, A FILTER WILL BE REQUIRED FOR EACH LEAD.

NOTE: DISCONNECTING THE ELECTRICAL CONNECTOR AT THE TRANSMISSION WILL SET THE TRANSMISSION DIAGNOSTIC CODES. IT WILL BE NECESSARY TO REMOVE THESE CODES AFTER THE CORRECTIVE ACTION HAS BEEN PERFORMED.

IMPORTANT: DISCARD THE INSTRUCTIONS IN THE FILTER PACKAGE. THIS FILTER IS AN IN-LINE FILTER WITH A SINGLE LEAD ON ONE END AND TWO LEADS ON THE OTHER END (ONE LEAD BEING BLACK (GROUND)). INSTALL THIS FILTER AS CLOSE TO THE PCM/TCM CONNECTOR AS POSSIBLE. IT IS IMPORTANT TO INSTALL THE FILTER WITH THE SINGLE LEAD END GOING TOWARD THE PCM/TCM AND THEN TAKE THE BLACK (GROUND) LEAD BACK AND ATTACH IT TO THE CASE OF THE PCM/TCM. IF THIS FILTER IS INSTALLED INCORRECTLY, THE CONDITION WILL BECOME WORSE.

SERVICE PARTS INFORMATION:

P/N DESCRIPTION QUANTITY 1224205 IN-LINE FILTER 1

PARTS ARE CURRENTLY AVAILABLE FROM GMSPO.

WARRANTY INFORMATION:

FOR VEHICLES REPAIRED UNDER WARRANTY, USE:

LABOR OP DESCRIPTION LABOR TIME N6360 WIRING AND/OR CONNECTOR - REPAIR USE PUBLISHED INSTRUMENT PANEL LABOR OPERATION TIME

FIGURES: 0

GENERAL MOTORS BULLETINS ARE INTENDED FOR USE BY PROFESSIONAL TECHNICIANS, NOT A "DO-IT-YOURSELFER". THEY ARE WRITTEN TO INFORM THOSE TECHNICIANS OF CONDITIONS THAT MAY OCCUR ON SOME VEHICLES, OR TO PROVIDE INFORMATION THAT COULD ASSIST IN THE PROPER SERVICE OF A VEHICLE. PROPERLY TRAINED TECHNICIANS HAVE THE EQUIPMENT, TOOLS, SAFETY INSTRUCTIONS AND KNOW-HOW TO DO A JOB PROPERLY AND SAFELY. IF A CONDITION IS DESCRIBED, DO NOT ASSUME THAT THE BULLETIN APPLIES TO YOUR VEHICLE, OR THAT YOUR VEHICLE WILL HAVE THAT CONDITION. SEE A GENERAL MOTORS DEALER SERVICING YOUR BRAND OF GENERAL MOTORS VEHICLE FOR INFORMATION ON WHETHER YOUR VEHICLE MAY BENEFIT FROM THE INFORMATION.